I've basically got the exact same issue. But sometimes even a hard reboot doesn't do the job.
My early 2011 MacBook Pro heats up dramatically but is only showing a blank white screen. Usually a PRAM reset and/or a safe mode start does the job but not all the time. I have copied the log from the console last time this has happened when trying to play Hearthstone:
29.10.14 23:51:28,789 Hearthstone[347]: WARNING: The Gestalt selector gestaltSystemVersion is returning 10.9.0 instead of 10.10.0. Use NSProcessInfo's operatingSystemVersion property to get correct system version number.
Call location:
29.10.14 23:51:28,790 Hearthstone[347]: 0 CarbonCore 0x9a5257e7 ___Gestalt_SystemVersion_block_invoke + 135
29.10.14 23:51:28,790 Hearthstone[347]: 1 libdispatch.dylib 0x9830a130 _dispatch_client_callout + 50
29.10.14 23:51:28,791 Hearthstone[347]: 2 libdispatch.dylib 0x9830a0b5 dispatch_once_f + 251
29.10.14 23:51:28,791 Hearthstone[347]: 3 libdispatch.dylib 0x9830b0d8 dispatch_once + 31
29.10.14 23:51:28,791 Hearthstone[347]: 4 CarbonCore 0x9a4b7fb8 _Gestalt_SystemVersion + 1050
29.10.14 23:51:28,791 Hearthstone[347]: 5 CarbonCore 0x9a4b7b69 Gestalt + 150
29.10.14 23:51:28,791 Hearthstone[347]: 6 Hearthstone 0x008cf342 _ZNK5Unity10GameObject15QueryComponentTI9TransformEEPT_i + 1728512
29.10.14 23:51:30,380 Hearthstone[347]: not in fullscreen state
The last entry seems especially weird since Hearthstone is set in fullscreen mode but this has been the moment when the screen went brown (this time, other colors: white most of the time, black and blue).
Any help would be appreciated.